1. Field of the Invention
The present invention relates to a swirl generator, particularly to a swirl generator with improved axial vanes.
A burner is one of the most important parts in a combustion system. The capability of the burner not only has great influence on the combustion efficiency of the system but also closely relates to the stability of the flame, the effective application of the fuel and the discharge of pollutants.
Improper combustion technology and improper selection of burners not only decreases the effective use of energy, but also results in air pollution by emitting large amount of hazardous combustion products.
2. Description of Related Art
Conventional burners employ a fan or a compressor to send the air into the combustion chamber to mix with the fuel for burning. The blades of the fan of such a conventional burner are of a fixed radial type. In practice, these devices are often operated with low excess-air combustion technics in industrial boilers. Specifically, by means of fuel gas recirculation, the peak temperature of the flame of the burner can be reduced to control thermal-NO. Controlling fuel-rich combustion, reducing peak temperature of flame, controlling residence time of combustion gas and partial fuel-rich combustion and increasing stability of flame are several important keys of advanced burner design. A swirling flow generated by properly-designed swirl generator and fuel-gas recirculator can control the residence time of combustion gas and the flame temperature.
When air flows through the fixed radial flow-guiding vanes to form a swirling flow, if the pressure drop and turbulent intensity are too high, then the capability of the burner will be poor.
Therefore, a good swirl generator must have a low pressure drop, low turbulent intensity and be capable of producing desired recirculation strength and controlling partial fuel-rich combustion, lowering peak temperature, controlling residence time of combustion gas and increasing flame stability.
The swirl generator of this invention can produce swirling flow to change the speed of air flow and deflect the axial incoming flow to produce a divisional angular vector. The swirling air flow then passes through an expansion quarl to form the recirculation flow.
Generally, there are three manners of generating swirling flow field:
1. manner of tangential entry; PA0 2. manner of guided vanes; and PA0 3. manner of rotating pipe.
In this invention, axial vanes are used to produce the required swirling flow field.
When the swirling flow passes through the combustion chamber, bluff body and expansion chamber, the swirling air flow will create reverse pressure gradient to form a recirculation zone. Not only is fuel vigorously mixed with air around this recirculation zone, but also a portion of the hot combustion product gas is recirculated back to sustain proper ignition, thereby assuring flame stability.
The swirling flow has the good quality of increasing flame stability. The proper swirling flow generated by properly-designed swirl generator can control flame, maintain fuel-rich combustion, reduce peak temperature of flame, control residence time of combustion gas, inhibit creation of NOx and increase combustion efficiency.
The axial vanes with fixed rotary angle of this invention are adapted to achieved desired the swirl level under the lowest pressure drop and the lowest turbulent intensity. To accomplish this goal, some extent of overlapping of the axial vanes must exist. Generally, the overlapping is about 30.degree.. However, the range from 20.degree. to 45.degree. is also available so as to insure the complete deflection of the air flow. Moreover, the arch shape of the axial vanes is used to substitute for general plane vanes to produce swirling flow so as to prevent the shortcomings of high pressure drop and high turbulent intensity.